Light-emitting diodes (LEDs) are widely used as a semiconductor lighting source. Generally an LED die is packaged by attaching it to a dielectric substrate, wire-bonding it to electrodes pre-installed on the substrate surface, and covering it with an epoxy “glob-top” to protect the LED die from mechanical damage and contamination, and to improve the LED radiation angle.
Performance of an LED is sensitive to the temperature of the operating environment. When an LED operates in high ambient temperatures, it can overheat and eventually malfunction or fail. The LED efficiency can be increased by improving thermal dissipation from the LED die. This can be achieved by the use of a circuit board with a high thermally-conductive substrate, such as a Metal Core Printed Circuit Board (MCPCB).
The circuit board thermal dissipation can also be increased by providing a metal pad on the circuit board surface and/or providing a metal plate on the bottom of the LED package. In this regard, the LED package may be placed directly on the circuit board so that it is in direct contact with a circuit board metal pad. Additionally or alternatively, the LED package may have a metal plate and be placed directly on the circuit board so that the LED package metal plate is in direct contact with the dielectric layer.
FIG. 1 depicts a prior-art circuit board structure 1 to support an LED package. A metal substrate 2 is covered with a dielectric layer 3. Electrode pads and conductive leads 5 are formed over the dielectric layer 3. A thermally-conductive LED pad 7 is positioned on the dielectric layer 3 to have direct physical contact with the bottom of the LED package.
FIG. 2 depicts an LED package 9 having an LED die 11 wire-bonded by wires 13 to pre-installed electrodes 15. The LED die 11 is positioned on a dielectric substrate 17 that has a metal plate 19 attached to its bottom. An optical lens 21 covers the LED die 11 and the wires 13.
FIG. 3 depicts a combination of the LED package 9 with the circuit board structure 1. The LED package 9 is positioned on the circuit board structure 1 so that the metal plate 19 is in direct contact with the metal pad 7. The electrodes 15 are soldered to the electrode pads 5. In this prior art device, however, the dielectric layer 3 separates the metal plate 7 from the metal substrate 2 and interferes with temperature exchange.